1. Field of the Invention
The present invention relates broadly to multi-chip modules and other similar electronic microcircuitry and methods of manufacturing the same. More particularly, the present invention concerns a multi-chip module comprising a low-temperature co-fired ceramic substrate having a first side on which are mounted active components and a second side on which are mounted passive components, wherein this segregation of components allows for hermetically sealing the active components with a cover while leaving accessible the passive components, and wherein the passive components are secured using a reflow soldering technique and are removable and replaceable so as to make the multi-chip module substantially programmable with regard to the passive components.
2. Description of the Prior Art
Many electronic systems include microcircuits designed for a specific product application. Unfortunately, both the active components and the passive components of such a microcircuit must typically be irreversibly committed to a particular design early in the microcircuit""s development cycle. As a result, if one or more of these components of the original design do not produce desired results, a new design cycle must be initiated.
A multi-chip module (MCM) is a type of microcircuit, and typically includes a number of active components, such as, for example, integrated circuits (ICs), transistors, and diodes, and a number of passive surface mount components, such as, for example, capacitors, resistors, inductors, or memory modules, electrically interconnected with high-density lines. The active components are typically interconnected by wire bonding to ceramic substrates (MCM-C), laminate substrates (MCM-L), or deposited thin film substrates (MCM-D). Both the active and the passive components are typically mounted on one side of the substrate so as to be intermingled in a non-segregated manner, and then hermetically sealed beneath a cover.
Unfortunately, prior art MCMs suffer from a number of problems and disadvantages, including, as mentioned, that both the active and the passive components, being sealed beneath the cover, are substantially inaccessible. As a result, where the design is later determined to be flawed, the MCMs cannot be modified to a new design and must be discarded. Furthermore, intermingling the active and the passive components can result in longer electrical interconnections which results in a correspondingly slower processing speed.
Due to the above-identified and other problems and disadvantages in the art, a need exists for an improved microcircuit that better facilitates efficient and convenient design, testing, and modification.
The present invention overcomes the above-described and other problems and disadvantages in the prior art with an MCM manufactured so as to allow for substantial programmability in that at least some of a plurality of components of the MCM are and remain removable and replaceable throughout the design and testing process.
In a preferred embodiment, the MCM broadly comprises a substrate; one or more active components; a cover; and one or more passive components. The substrate is a low-temperature co-fired ceramic (LTCC) substrate, and presents a first side and a second side. The active components can include ICs, transistors, and diodes and are wire bonded to the first side of the substrate. The cover protects the mounted active components by hermetically sealing over them. The passive components are, for example, capacitors, resistors, inductors, or memory modules, and are reflow soldered to the second side of the substrate. Thus, the passive components are not hermetically sealed under the cover, and therefore remain accessible.
The active and the passive components are electrically interconnected with vias or through-holes in the substrate or with edge connectors. Because the active and the passive components are not mounted or otherwise secured in an intermingled and non-segregated manner on the same side of the substrate, the electrical interconnections between the active components are not required to avoid the passive components or otherwise be longer than absolutely necessary and can therefore be made shorter than is typically possible in prior art MCMs. These shorter interconnections advantageously result in correspondingly improved performance.
The described MCM can be designed, tested, and modified as follows. First, an interconnection network is fabricated on the substrate. Then the active components are attached and wire bonded to the first side of the substrate. Next, the active components are hermetically sealed under the cover. Then the passive components are mounted to the second side of the substrate using a reflow soldering technique which allows for removing and replacing the passive components as desired. Next, the MCM is tested for a desired performance. Lastly, as desired, certain of the passive components can be removed and replaced using conventional solder reworking techniques so as to achieve the desired performance. With special test fixtures, the passive components can be left off the MCM, and the MCM can be functionally tested. Passive components can then be selected and attached to the MCM for a specific circuit design.
Thus, it will be appreciated that the present invention provides a number of substantial advantages over the prior art, including, for example, segregating the passive components from the hermetically sealed active components, thereby facilitating removal and replacement of the passive components and making the MCM substantially programmable. This advantageous ability allows developers to test a variety of component values prior to committing to a finalized design, thereby shortening total design cycle time by minimizing circuit redesign and rebuild time. Furthermore, this segregation of components facilitates shorter electrical interconnections to result in correspondingly improved performance for the active components.
These and other important features of the present invention are more fully described in the section titled DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT, below.